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 Post subject: How are Lasers Used in Diamond Cutting
PostPosted: Mon Jan 27, 2014 8:54 pm 
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Here is an encompassing post from Michael Hing on the subject of lasers and Diamond Cutting:

As well as 'laser sawing', which is actually now much more common than conventional sawing, they can also be used instead of bruting, and for shaping complex outlines. It is, for example, possible to simply laser a heart-shaped outline instead of having to perform several complex pre-shaping operations. You can also use a laser to create a cone-shape to reduce the amount of polishing that is required. Lasers have the advantage of creating 'off-cuts' (rather than grinding waste away into powder, which is what mechanical processes usually do). The off-cuts can be polished or re-sold to make tiny diamonds.

Lasers are also extensively used for marking guidelines on the surface of the stone (to tell the polisher to keep polishing a certain facet at a certain angle until it hits a certain target). These guidelines are very fine, thin, blackened straight or dotted lines on the surface of the rough stone a few microns deep/wide. However, the planner sometimes changes his or her mind during the process. For example, a stone may hypothetically have been marked for sawing as a 1ct round major stone and a 0.5ct minor stone, only for the planner or their quality controller to subsequently realise that they could get a better price from two 1ct ovals instead. The stone would then be re-marked in a different place and the polisher instructed accordingly, but the original laser lines are still etched on the surface and, if the stone is 'tight' for that all-important 1ct weight, the polisher may not be able to polish away all of the remnants of the original markings whilst retaining the target weight. We had pictures of a stone on Gemtalk some time ago which displayed traces of dotted lines along the girdle which are the result of this decisionmaking process.

Another problem with lasers is that ultra-intense beams of light can behave unpredictably when they hit the surface of the diamond. You can paint the surface of the stone with a coating that helps the laser to be absorbed. After the initial impact, you tend to get a blackened, graphitised surface that absorbs subsequent laser passes quite well. However, some stones have a slightly etched sheen consisting of multiple micro-ridges and/or trigons and/or tetragons ('squaregons' like square trigons which you see on cuboid faces). These micro-ridges can be very well-defined, reflective and satin-like, and they can mess up the lasering process by refracting some of the beam's pulses into the stone unpredictably. This can cause graphitisation and damage in unpredictable places more or less anywhere on the stone.

The GIA attempts to distinguish between laser-drilling holes and laser marks on the surface that were unintentional remnants from the polishing process. They call the latter 'laser remnants' and will note them on the certificate as such - this is not regarded as a type of treatment. There's an example in the link below. Incidentally, there's nothing mysterious about the mark shown, it is an obsolete type of marking used by an Israeli company called Sarin Technologies that was used to help to align a rough stone with its corresponding 3D video-scan under liquid selenium immersion for a diamond inclusion-plotting and polish-planning system called Galaxy (I gather that the latest version of Galaxy uses smarter computer processing to simply match the rough stone's outline with the outline of the video picture, so these 'anchoring marks' are no longer needed).

http://www.gia.edu/cs/Satellite?c=Page& ... 5961484393

Further info here...
http://www.jckonline.com/2006/10/07/gia ... g-remnants

Incidentally, if you have something like a briolette that has been laser-drilled to create a hole through the stone for mounting, this will be reported as a 'mounting feature'. This is quite rare, but here's an example, click on the certificate and then click again to enlarge the picture and read the comment (note that the stone was classified as 'internally flawless', indicating that the hole through the tip was classified as a polish feature rather than a clarity feature despite being clearly visible to the naked eye - which seems fair in my opinion, as otherwise how would you set it?).

http://www.christies.com/lotfinder/jewe ... 09c081ef6e

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